You may have once had doubts that the American left has spent decades feeding a weed that would grow to strangle American liberty.

But those doubts have now been dispelled, haven't they?

Because a new survey of American college students by the Brookings Institution offers perhaps the most depressing forecast of the future of liberty that we've seen.

It tells us that many of the most privileged people on the planet, American college students, are barbarously illiterate when it comes to understanding the freedoms given them by the Constitution.

A barbarously illiterate people can easily be turned into an angry horde. It is dangerous work, yes, but it can be done. They can be herded, cynically, with prompts to emotion and calls to anger for short-term political gain.

But having thrown away their understanding of their freedoms, such people cannot remain free for long.

According to the survey, when asked if the First Amendment protected so-called hate speech, 44 percent of college students said no.

And 16 percent said they didn't know the answer.

More than half, 51 percent, said they think that "shouting so the audience can't hear," also known as the heckler's veto, is an acceptable tactic for silencing a controversial speaker.

So just shout them down. Scream. Don't engage, don't ignore, and don't bother to use reason and offer counter arguments to win the battle of ideas.

Instead, shout with venom. Shout with feeling. Shout with power and shout with anger so that those doing the herding can goad you into the chutes. And when many shout together, even to silence ugly viewpoints, here's what happens: Their faces become contorted, and spittle flies from the corners of their mouths. This is not what a free people in a republic looks like. This is what a mob looks like.

Perhaps most ominous of all, according to the survey, 19 percent of students believe that violence is an acceptable response to ideas they don't like.

That is an astounding number: 1 in 5 college students is possessed of the belief that it is OK to club your opponents down.

I hope that number is wrong. I hope that once the survey by John Villasenor, of the University of California at Los Angeles, is offered up to peer review, something in the methodology will be found amiss. But I doubt it.

And yes, the survey received financial support from the conservative Charles Koch Foundation, which will allow the left to cry foul.

But we've all seen thuggery on college campuses in the news, and the silencing of dissent and the attention to safe spaces, so given all that, the survey results aren't really that surprising.

We've seen those professors, even liberal professors, psychically or physically intimidated, even injured, by the antifa thugs of the left.

And we've seen, with but a few exceptions, the relative silence from Democratic political leaders and liberal pundits, who may not embrace the violence, but embrace the use of raw emotions for political advantage and internet clicks.

What's the matter, guys? Crickets got your tongue?

To say that all this is chilling doesn't quite do it justice. It is monstrous. And we can see that weed growing.

These college students aren't the enemy. They are our sons and daughters, our nieces, nephews, friends, contemporaries.

But they are the future leaders of our nation, among them will come our politicians, judges, intelligence officers, prosecutors, administrators and information technology engineers overseeing how Americans receive their political news.

And sadly, it is clear that too many have a fundamental misunderstanding of the Constitution, particularly of the First Amendment that protects all American liberty.

Some speech is called hateful because it is indeed hateful, and racist and bigoted. Who likes or appreciates bigoted speech? No civilized person appreciates it. We loathe it.

But it is still zealously protected by the Constitution. Why?

Because if even hateful speech isn't protected, we allow our freedoms to be killed off.

It is far too easy to apply the "hate speech" tag to other kinds of speech, called hateful only because it is politically unfashionable. Some of it is subversive, threatening those in power, and those in power already let loose their dogs to bark and shame and shout the subversives down. That's politics. What's not acceptable is thinking that government has the right to shut speech down.

In a nation founded on liberty, it is understood that we can't regulate political speech, even if it's hateful, because having the government regulate speech would end all speech.

It would allow partisan politics to ooze in, like sepsis in a wound, and regulate out any ideas that the elites find threatening.

So we allow Black Lives Matter and other protesters to shout out their animus toward police, "Pigs in a blanket/Fry 'em like bacon," and we allow Nazis and the KKK and those white boys with the tiki torches in Virginia to shout their alt-right hatred of minorities and others.

We protect their speech, hateful as it is, to protect our own.

That's how we've kept ourselves free, by adhering to the First Amendment of America's most sacred document, the Constitution.

How did so many college students not learn this before college? How did so many not learn this in their K-12 educations?

Such profound ignorance didn't just spring fully formed from some political forehead. It has been reinforced. They've already been herded.

It has been taught to them by indifferent parents, by a corrosive entertainment/media culture, and perhaps most importantly by their high school teachers, who have groomed them for this.